Many uses of vehicles, particularly service vehicles, require provision for utilizing power developed by the vehicle engine for driving some sort of component such as a compressor, pump, generator, winch or the like, in addition to providing power for motive purposes. While in some cases the components are electrically driven by electrical motors powered by the vehicle electrical system, much higher levels of power to drive such components can be achieved by coupling the engine driven components mechanically or hydraulically to the engine mainshaft to be directly driven thereby.
Presently, direct coupling as mentioned immediately preceding is achieved in one of three basic ways. A first is so-called "underhood mounting". According to this method, a bracket is bolted to the engine block and in turn mounts a hydraulic pump, compressor or other engine driven component. The component is then driven by means of a belt connected to the engine mainshaft, frequently via an electrically operated clutch or the like. While this method works well for its intended purpose, many modern vehicles have insufficient space under the hood in which the engine driven component can be suitably installed, particularly when the component is a large capacity device.
A second method is to utilize a so-called "PTO" or power take-off. In this form, a PTO unit is bolted to the vehicle transmission. A hydraulic pump or a drive shaft connected to the PTO is used to drive the engine driven component by means of a hydraulic motor or a direct mechanical connection respectively. This system again works well for its intended purposes but is generally limited to relatively large vehicles whose transmissions are provided with a PTO unit. Thus, this method is not universally applicable because many smaller vehicles do not have a PTO.
A third method is the use of a so-called split shaft transmission. The main drive shaft of the vehicle is split and a split shaft transmission device placed in line between the two parts of the drive shaft. The split shaft transmission device provides PTO outlets and allows disconnection of the engine from the drive wheels of the vehicle to operate PTO outlets. Again, this method works well but it is complicated and expensive.